1. Field
Apparatuses and manufacturing methods consistent with the present invention relate to an optical module for a high-speed and large-volume optical communications system, and to a method of packaging the same.
2. Description of the Related Art
Along with the spread of the Internet, the development of a high-speed and large-volume optical communication system has been achieved. Especially in a long-distance and large-volume communications system, efforts have been made to reduce wavelength fluctuation (hereinafter referred to as “wavelength chirping”), which occurs during modulation, because such wavelength chirping limits the transmission distance. A frequency pulse laser (FP laser) of end-surface light emission type is used for short-distance and small-volume communication, and a distributed feed back laser (DFB laser) which oscillates in a single-mode is used for communication with a speed of several Gigabits per second (Gb/s). Generally, in a case of a transmission for a distance of tens of kilometers with a transmission speed of 10 Gb/s, the laser is not directly modulated, but the laser is caused to oscillate continuously. And the modulation is performed by use of an external modulator.
In an optical module disclosed in the U.S. Pat. No. 6,963,685, light from a directly modulated DFB laser is passed through an optical filter and, thus, converts a frequency modulation component to an amplitude modulation component. This optical module equalizes waveforms by the additional use of wavelength dispersion of the filter. However, the optical module as described in this related art requires its optical axis to be adjusted when the DFB laser and the optical filter are packaged in the optical module. This does not allow passive alignment to be applied to the structure of the optical module. Without such passive alignment, the cost and the time for manufacturing the module will increase.
The U.S. Patent Application Publication No. 2005/0175356 discloses that a waveguide ring resonator is used as the optical filter. However, the optical module as shown in this related art also requires improvement of the structure for packaging the DFB laser and the optical filter as in the case of the optical module in the previous related art, U.S. Pat. No. 6,963,685.
In a case of an optical module as shown in “Chirp-managed Directly Modulated Laser (CML)”, IEEE Photonics Technology Letters, Vol. 18, No. 2, Jan. 15, 2006, using an optical filter which has periodical wavelength characteristics by using a multiple etalon is disclosed. And thus, a frequency modulation signal is converted to an amplitude modulation signal by using a slope of this optical filter. However, the use of the etalons as an optical filter requires the optical axis to be adjusted. And, this does not allow passive alignment to be applied to the structure of the optical module.
An optical module shown in “Error-free 250 Km transmission in standard fiber using compact 10 Gb/s chirp-managed directly modulated lasers (CML) at 1550 nm”, Electronics Letters, 28 Apr. 2005, Vol. 41, No. 9, realizes a 250 Km transmission by extending the transmission distance of the optical module as shown in previous related art, “Chirp-managed Directly Modulated Laser (CML)”. However, this optical module is too large to meet the requirement of miniaturization of the module. This is because etalons are used as a filter of the optical module.